The effect of vitamin D supplementation on peripheral regulatory T cells and β cell function in healthy humans: a randomized controlled trial

Background Increasing evidence supports the role of vitamin D (vitD) in modifying the risk to develop type 1 diabetes (T1D) and other autoimmune diseases. VitD3 might stimulate regulatory T cells (Tregs), a central player in the maintenance of self-tolerance. In addition, direct effects of vitD on beta-cell function are postulated. The aim of our study was to evaluate the effect of a high dose vitD supplementation on Tregs frequency (% Tregs) and beta-cell function assessed by a mixed meal tolerance test (MMTT) in healthy humans. Methods A double-blind, placebo controlled trial was performed in 59 healthy adult subjects (49% females). Subjects received oral vitD3 (140 000 IU monthly) or placebo for 3 months. % Tregs within 20 000 CD4(+) T cells of peripheral blood was determined by multi-parametric FACS-analysis. A liquid MMTT was carried out before and after treatment. Results %Tregs increased significantly in the vitD group, but remained unchanged in the placebo group. Fasting C-peptide concentrations did not change significantly in either group. Similarly, the mean AUC for C-peptide after 3 months and the change in mean values from baseline to the end of the treatment were comparable in both groups. Conclusions A short time high dose vitD3 supplementation significantly increased the frequency of Tregs, but did not further improve beta-cell function in apparently healthy subjects. The immunomodulatory potential of vitD might be an important mechanistic link for the association of vitD and T1D. Copyright (C) 2011 John Wiley & Sons, Ltd.